title: Prohibitin (PHB) inhibits apoptosis in rat granulosa cells (GCs) through the extracellular signal-regulated kinase 1/2 (ERK1/2) and the Bcl family of proteins.
abstract: Mammalian ovarian follicular development is tightly regulated by crosstalk between cell death and survival signals, which include both endocrine and intra-ovarian regulators. Whether the follicle ultimately ovulates or undergoes atresia is dependent on the expression and actions of factors promoting follicular cell proliferation, differentiation or apoptosis. Prohibitin (PHB) is a highly conserved, ubiquitous protein that is abundantly expressed in granulosa cells (GCs) and associated with GC differentiation and apoptosis. The current study was designed to characterize the regulation of anti-apoptotic and pro-apoptotic factors in undifferentiated rat GCs (gonadotropin independent phase) governed by PHB. Microarray technology was initially employed to identify potential apoptosis-related genes, whose expression levels within GCs were altered by either staurosporine (STS) alone or STS in presence of ectopically over-expressed PHB. Next, immunoblot studies were performed to examine the expression patterns of selective Bcl-2 family members identified by the microarray analysis, which are commonly regulated in the intrinsic-apoptotic pathway. These studies were designed to measure protein levels of Bcl2 family in relation to expression of the acidic isoform (phosphorylated) PHB and the components of MEK-Erk1/2 pathway. These studies indicated that over-expression of PHB in undifferentiated GCs inhibit apoptosis which concomitantly results in an increased level of the anti-apoptotic proteins Bcl2 and Bclxl, reduced release of cytochrome c from mitochondria and inhibition of caspase-3 activity. In contrast, silencing of PHB expression resulted in change of mitochondrial morphology from the regular reticular network to a fragmented form, which enhanced sensitization of these GCs to the induction of apoptosis. Collectively, these studies have provided new insights on the PHB-mediated anti-apoptotic mechanism, which occurs in undifferentiated GCs through a PHB → Mek-Erk1/2 → Bcl/Bcl-xL pathway and may have important clinical implications.
authors.affiliation: Department of Obstetrics and Gynecology, Reproductive Science Research Program, Morehouse School of Medicine, 720 Westview Drive Southwest, Atlanta, GA, 30310, USA.
authors.forename: Indrajit
authors.initials: I
authors.lastname: Chowdhury
authors.forename: Winston E
authors.initials: WE
authors.lastname: Thompson
authors.forename: Crystal
authors.initials: C
authors.lastname: Welch
authors.forename: Kelwyn
authors.initials: K
authors.lastname: Thomas
authors.forename: Roland
authors.initials: R
authors.lastname: Matthews
mesh_terms: D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D002454:Cell Differentiation; D045304:Cytochromes c / Q000378:metabolism; D005260:Female; D006107:Granulosa Cells / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism; D020935:MAP Kinase Signaling System; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism; D010053:Ovary / Q000166:cytology / Q000378:metabolism; D000091402:Prohibitins; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C000717332:Phb protein, rat; D000091402:Prohibitins; D019253:Proto-Oncogene Proteins c-bcl-2; D012097:Repressor Proteins; D051020:bcl-X Protein; D045304:Cytochromes c; D053148:Caspase 3